Abel, Darrel, author
Barron's Educational Series, 1963
Buku Referensi
United State Information Agency, 1994
Buku Teks
VanSpanckeren, Kathryn, author
Lembaga Penerangan Amerika Serikat, 2001
Buku Teks
edited by Hennig Cohen
Basic Book, 1969
Buku Teks
Wachner, Clarence W., author
Macmillan, 1963
Buku Teks